This invention relates generally to a fingerprint image processing apparatus, and more particularly to an apparatus and a method for removing moisture from contact surfaces of such apparatus, or from the finger of a subject to be imaged, or from both.
Originally, fingerprinting was done by inking a suspect's finger and applying the inked finger to paper. As can be readily understood, fingerprint information in this form was difficult to use. Making a fingerprint match was an extremely time-consuming task. Digital technology significantly advanced the art of fingerprinting. Inked images could be scanned, the image digitalized and recorded in a manner that could later be searched in a reasonably expeditious manner by computer. Problems arose, however, due to the quality of inked images. Over- and under-inking resulted in blurred or vague images, thus rendering the digitalized information useless. Further, the process of scanning an inked image was relatively time consuming.
These and other problems led to "live scanning." According to live scanning techniques, the fingerprint of a suspect is scanned directly from the suspect's finger, as opposed to being scanned from an inked image of the print. More specifically, live scans are those procedures which capture fingerprint ridge detail in a manner which allows for the immediate processing of the fingerprint image with a computer. Original work in the field dates back to original patents filed in 1964 concerning techniques used to capture high contrast images of fingerprint for photographic or digital capture of fingerprints.
Since their introduction, live scans have become an important tool for law-enforcement. The live scan has the potential to overcome inherent weaknesses in the ink capture of fingerprints. In particular, live scans are advantageous because they reduce over- or under-inking; reduce smudging or smearing; provide immediate transmission of fingerprint images; and allow for image enhancement if necessary.
These characteristics provide law-enforcement with the ability to improve the quality of the fingerprint data base, thereby improving the likelihood that identifications can be made either from latent fingerprints or from identity verification checks.
Fingerprint image processing systems have been disclosed in the literature and in patents. An example of one type of image processing system is shown in U.S. Pat. No. 4,322,163 to Schiller. Schiller '163 discloses an optical assembly for fingerprint image generation, which includes a reflective layer incorporated between a resilient layer and a flat glass base or platen. The force transmitted by a finger pressed against the back surface of this platen will cause the resilient layer to deform and provide a scannable image. Digital Biometrics, Inc. has recently published brochures describing an apparatus for obtaining a fingerprint image through a hard prism. Contact by a finger with a planar surface of the prism results in a high contrast image reflected onto sensor means for processing of the fingerprint image.
Generally, as can be understood from the discussion above, known fingerprint imaging apparatus and methods involve placement of one or more of the fingers of a human subject onto a surface which is then scanned to provide an image of the fingerprint. As can be readily understood, the process of being arrested can be particularly stressful, and it has been found that individuals often perspire while being fingerprinted. It has also been found that the presence of such perspiration, sweat or other moisture on the subject's finger or fingers, or on the contact surface, during image processing results in an image of reduced clarity. The image may, in fact, be so distorted as to be of little or no use in identification. More specifically, perspiration affects the dielectric surface properties of the finger. The effect is an optical, or electromagnetic phenomenon which distorts the fingerprint image.
Accordingly, it is an object of the present invention to provide a method and an apparatus suitable for removing such perspiration or other moisture from the finger or fingers of the subject, and/or from the contact surface itself.